The present invention relates to a signal processing circuit which is responsive to a detection signal of a yaw-rate sensor so as to remove a noise component of the detection signal indicative of a yaw rate occurring with respect to a motor vehicle.
A conventionally yaw-rate sensor comprises a piezoelectric element such as disclosed in the U.S. Pat. No. 4,628,734 in which a plate-like driving piezoelectric device and a plate-like detecting piezoelectric device are arranged and coupled so as to be parallel to a detection axis and perpendicular to each other. With this arrangement, the plate-like driving piezoelectric device vibrates in response to application of an alternate-current drive voltage thereto. At this time, an angular velocity (rate) can be obtained by detecting a bending state of the plate-like detecting piezoelectric device in a direction perpendicular to the vibrating direction. Further, various yaw-rate sensors are known, such as a gas-rate sensor.
Here, on the detection signal of the yaw-rate sensor there is generally superimposed a noise component (high-frequency component) due to mechanical vibration and electrical noise, and therefore a process is required to eliminate the noise component. The conventional eliminating process of the noise component is effected by using an active filter (low-pass filter) constructed by an operational amplifier or a moving average type or recursive type digital filter (low-pass filter). However, there is the possibility that a noise with a sharp peak (spear-like noise) is superimposed on the detection signal of the yaw-rate sensor or a rapid signal variation occurs at the abnormal time such as a sensor fail. In such a case, difficulty is encountered to sufficiently eliminate the noise component by means of the aforementioned active filter or the aforementioned moving average type or recursive type digital filter. Further, in the case of increasing the order number of the filter, the active filter causes the circuit to becomes complex to increase the cost and the digital filter causes the calculation time to be taken largely to allow the phase lagging of the detection signal.